The manufacture of many types of work pieces requires the substantial planarization or polishing of at least one surface of the work piece. Examples of such work pieces that require a planar surface include semiconductor wafers, optical blanks, memory disks, and the like. One commonly used technique for planarizing the surface of a work piece is the chemical mechanical planarization (CMP) process. The terms “planarization” and “polishing,” or other forms of these words, although having different connotations, are often used interchangeably by those of skill in the art with the intended meaning conveyed by the context in which the term is used. For ease of description such common usage will be followed and the term “chemical mechanical planarization” will generally be used herein with that term and “CMP” conveying either “chemical mechanical planarization” or “chemical mechanical polishing.” The terms “planarize” and “polish” will also be used interchangeably. The CMP method typically requires the work piece to be loaded into and mounted precisely on a carrier head in a manner such that the surface to be planarized is exposed. The exposed side of the work piece is then held against a polishing pad and relative motion is initiated between the work piece surface and the polishing pad in the presence of a polishing slurry. The mechanical abrasion of the surface caused by the relative motion of the work piece with respect to the polishing pad combined with the chemical interaction of the slurry with the material on the work piece surface ideally produces a planar surface. Typically the work pieces are processed in batches or lots that include a plurality of work pieces. For example, with the CMP processing of semiconductor wafers, each of the wafers in a lot must be sequentially loaded from a wafer cache onto the carrier head for planarization. Following the planarization, each wafer is unloaded from the carrier head and again placed in a wafer cache, or is transferred to another carrier head for further processing, or is transferred to a subsequent processing apparatus such as a cleaning station.
The CMP processing of work pieces can be a slow process, especially because the work pieces must be processed individually rather than in batches. To provide for a high throughput for a manufacturing process that includes a CMP step, a number of CMP systems must therefore be provided to process a number of work pieces in parallel. Present CMP systems, although functional and capable of producing the desired end result of planar work piece surfaces, have been large, inefficient users of manufacturing area floor space. It is impractical to increase manufacturing capacity by arbitrarily adding additional CMP systems because manufacturing area floor space is expensive and adds to the overall cost of manufacture of the work piece.
Accordingly, it is desirable to provide a chemical mechanical planarization (CMP) apparatus that overcomes the shortcomings of prior art CMP apparatus and allows efficient use of manufacturing area floor space and yet is efficient to maintain and operate. In addition, it is desirable to provide an efficient method for polishing the surfaces of a plurality of work pieces. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.